run_shell_command blocking forever

When I was building some utility scripts, I kept running into problems with the git fetcher where it would block forever on fetching a repository.  It was blocking on the readline() when I am pretty sure the git command was actually complete.  Switching to this method for retrieving the lines seems to fix it.  

It's also the method suggested by [a stackoverflow quesiton with a similar problem](http://stackoverflow.com/a/12471855/9805).  The question seems to indicate that this might happen if the called program finishes before the readline() starts.